Yoshitaka Nagahama is a professor at Institution for Collaborative Relations Ehime University, Japan. As a specialist in reproductive biology, Prof. Nagahama studies the molecular mechanism of sex determination/differentiation and gemetogenesis. His contribution includes the first identification of spermatogenesis-inducing hormone and oocyte/sperm maturation-inducing hormone using fishes. His achievement of complete spermatogenesis from spermatogonia to mature sperm under in vitro organ culture conditions provided extensive insights into understanding the entire events of spermatogenesis. The most important contribution for the field of sex determination is the identification of sex determining gene (DMY) in medaka, the second gene of this kind in any vertebrates. The finding of DMY is an important milestone in the evolution history of sex determination mechanism.